1. Field of the Invention
The present invention relates to metal-oxide based memory devices and methods for operating such devices.
2. Description of Related Art
Some metal-oxides can be caused to change resistance between two or more stable resistance ranges by application of electrical pulses at levels suitable for implementation in integrated circuits, thus providing a basis for use in nonvolatile resistive random access memory RRAM.
Metal-oxide based RRAM has attracted much attention because of its simple structure, high speed, low power consumption, and potential for 3D stacking.
In metal-oxide based memory, data is stored by applying energy pulses to the metal-oxide material to induce a change in resistance of the metal-oxide material between two or more resistance states including a low resistance state (LRS) and one or more higher resistance states (HRS).
Multi-level operation involves changing the resistance of the metal-oxide material between more than two resistance states and is desirable since the data storage density can be increased and the process costs can be reduced.
In order to reliably distinguish between the various resistance states, and thus properly determine the data value stored in a memory cell, it is important to maintain relatively large resistance windows between the states. However, endurance problems have arisen in metal-oxide materials due to instability of the resistance which reduces the resistance window between the various states, resulting in reliability issues and possible bit errors of the device.
It is therefore desirable to provide metal-oxide based memory devices and methods for operating such devices which address the endurance problems discussed above and result in improved reliability and data storage performance of the device.